The invention relates to a method for carrying out a location updating from a mobile cellular radiophone system, such as a DECT system, to another cellular radiophone system, such as the GSM mobile phone system, which mobile cellular radiophone system comprises at least one base station with at least one mobile terminal in its area, in which method the location area identity transmitted by the base stations of said other cellular radiophone system is observed at a mobile station of said other cellular radiophone system in order to determine when the mobile radiophone system moves from one location area to another in said other cellular network. The method according to the invention is intended to be used in particular when a DECT system located in a moving vehicle such as a train is connected with the GSM mobile phone system. The method according to the invention is however not limited to these particular systems but can be applied to connecting other similar networks as well.
The GSM (Groupe Special Mobile) is, as is well known, a pan-European mobile communication system. The GSM network is divided into national GSM networks, which have in their area one or more service areas, in each of which services are provided by one Mobile Services Switching Centre (MSC). A GSM service area for its part is divided into one or more Location Areas, each of them being an area covered by several cells. Each cell is serviced by one base station (BTS, Base Transceiver Station). More detailed information on the structure and functioning of the GSM system can be obtained e.g. from GSM specification 04.08, Ver. 3.11.0.
The DECT (Digital European Cordless Telecommunications) is a pan-European cordless phone system standard. Three typical environments where cordless phones are used are home, office and a so-called telepoint, which is a base station of the system. Base stations are located in public places for incoming or outgoing calls. A DECT terminal can be used to transmit not only speech but also data. More detailed information on the structure and functioning of the DECT system can be obtained e.g. from the specification DECT Common Interface, Part: Network Layer Ver. 8.00.
The holder of a DECT terminal may also be a client of a GSM network, in which case his terminal comprises the Subscriber Identity Module (SIM) of a GSM mobile phone or a corresponding functional block. The DECT system can also be located in a moving vehicle such as a train and be connected with a GSM mobile phone network by means of a radio path. In that case the basic problem is, however, that a call coming to the DECT terminal cannot be trunked to the destination, because in the DECT system the DECT location area does not change in the train although the GSM location area does as the train moves (location updating to the DECT system is effected in accordance with the specification on the basis of the DECT location area). The GSM system thus does not receive information on the presence of the DECT terminal and cannot, with respect to said DECT terminal, effect the location updating to the GSM network.